Pivoted cam follower



March 11, 1959 E. WQYDT PIVOTED CAM FOLLOWER 3 Sheets-Sheet 1 Filed March 31, 1955 FIG. 1

March 17, E. WOYD'I I PIVOTED CAM FOLLOWER Filed March 31, 1955 3 Sheets-Sheet 2 March 17, 1959 E. WOYDT 2,877,662

PIVOTEID CAM FOLLOWER Filed March 31. 1955 3 Sheets-Sheet 3 IN VENTOR United States Patent High-pressure pumps or high-pressure fluid motors are known wherein the piston bears on an eccentric or a swash plate by means of a pivotable sliding shoe. The sliding shoe then usually has a covering of bearing metal, and is adapted to the surface of the eccentric or swash plate. In high-pressure machines of the kind mentioned, the surface pressure between the sliding shoe and the eccentric or swash plate must be as high as possible for reasons of space. The surface pressure is periodically increased at the forward and rearward edges of the shoe, since the forces for pivotal acceleration of the shoe arise at these edges. They can consequently reach such a magnitude that the sliding surface is deformed in this region, so that the load capacity and life of the sliding shoe are reduced.

Rounding off the rearward edge of the sliding shoe, as successfully used in Michell bearings, for example for the axial support of turbines, can only mitigate the disadvantages and dangers referred to in sliding shoes on high-pressure pumps or motors of the type mentioned to an insubstantaial extent. In fact, in Michell bearings a state of inertia arises rapidly after starting, i. e. a certain oil-wedging angle arises between the sliding shoe and the support. Sliding shoes in pumps and motors of the present kind are, however, forced by the eccentric to keep readjusting themselves because of the continuously alternating application and removal of loading due to the reciprocating pivoting movement, without a lasting state of inertia being reached. The sliding shoe must,'in fact, like a shaft-riding member, execute a skipping motion each time the eccentric rotates, and can only adjust itself to the new state after the completion of said motion.

The invention is explained with reference to the accompanying drawings, in which Fig. 1 shows a vertical section through a piston and a sliding shoe according to the invention;

Fig. 2 shows a corresponding sectional side elevation of the piston and shoe, co-operating with an eccentric;

Fig. 3 shows diagrammatically in side elevation on a larger scale a sliding shoe of known type co-operating with an eccentric; and

Fig. 4 is a similar diagrammatic side view illustrating by way of comparison the present invention.

In these drawings, Figure 3 shows a sliding shoe 4 of the known type which co-operates with an eccentric 7 and is movable upwards and downwards in the direction of the line 1a, and pivots to and fro about point 1b, which goes up and down. During part of the revolution of the eccentric it moves anti-clockwise. When this part of the revolution of the eccentric is over, it must suddenly start pivoting clockwise. At this instant the forward end 4b takes up a relatively large clearance from the eccentric 7 so that the oil-wedging angle increases. This increase can become so great that the sliding shoe is for a short time only supported against the eccentric at the point X, i. e. at the point where the rearward rounding off of the sliding shoe begins. In this case the specific pressure between shoe and eccentric naturally increases to an extraordinary degree, illustrated by way of example by the curve k1. The oil wedge no longer holds to the right and left of the bases of this curve. However, the specific pressure at point X can be so great that the oil film is completely destroyed, so that the sliding surface of the sliding shoe is then damaged.

The purpose of the invention is to produce a construction which avoids or reduces the disadvantages named. This construction is distinguished above all by the fact that the surface of the sliding shoe is not completely adapted to the rotating member, which may be an eccentric or a swash plate, in the region of the rearward edge, but maintains some clearance throughout a length of M or more of the sliding surface (measured from the rearward edge) because a flat wedging angle of about 1 or less is formed between the surface of the sliding shoe and the eccentric or swash plate. It is known per se to provide such a clearance at the forward edge of the sliding shoe for the purpose of facilitating the entry of the lubricating oil.

Figure 4 explains the substantially more favourable oil' pressure conditions according to the invention expressed by the loading curve k2. While the sliding surface from X to Z is substantially adapted to the curve of the eccentric, it is at a distance over the length of X to Y, forming an oil-wedging angle with the surface of the eccentric. In this case, if the forward end 4a of the sliding shoe moves somewhat high, the shoe tilts about the point X. It is then subjected to a braking torque inthe sector X to Y which still rests on its oil wedge, said torque preventing further tilting until the point X- lies on the eccentric and breaks the oil film. There remains an oil wedge both in front of and behind the point X, so that the loading curve k2 results. It comprises approxi mately half the surface content of curve k1, does not reach the height of curve k1 at the point X, but on the contrary contains a much greater base width, i. e. the pressure between the eccentric and the sliding shoe is distributed in this case over a much greater surface, so that the oil film can never be broken at the point X. The length of the path X is approximately equal to or greater than one-fifteenth of the arcuate length of the sliding surface extending, from the rearward edge y to the leading edge A in order to achieve the desired effect.

It is possible for the first time by means of the invention, as long-term tests have shown, to transmit the forces between piston and eccentric in high-pressure pumps or high-pressure motors by means of one sliding shoe. The many diagrammatic proposals which have been made in this field have, on the contrary, so far not led to any practical use, since the sliding shoes were never developed to meet the stresses of continuous running, especially at their rear edges.

On the other hand, the danger can exist that any soft bearing metal used on the rearward edge of the sliding shoe will be squeezed away. This danger is removed in accordance with a further development of the invention by the fact that a bar of metal of greater hardness than that of the bearing metal covering limits the rearward edge of the sliding shoe, for example, in the region of the wedge angle. This bar can be in one piece with the sliding shoe, but for reasons of production is expediently inset in the form of a special strip.

The life of the sliding shoe is further influenced by the kind of lubrication. Consequently, in the sliding shoe according to the invention, care should be taken to provide uniform and copious lubrication over the whole width of the shoe, an oil spray pipe being arranged in front of the sliding shoe in such a manner that oil is sprayed uniformly over the whole width of the sliding shoe, for example from holes or slots disposed close beside one am with a further development of the invention a middle.

hinge eye is now provided on the sliding shoe, while the piston is given two lateral hinge eyes. T his development makes the sliding shoe lighter, which more particularly makes its inertiamoment smaller during oscillation about the hinge axis, so that the magnitude of the pivoting forces acting in the region of the edges of the sliding shoe be. comes smaller.

In a sliding shoe which bears on an eccentric the dc- I sired clearance between sliding shoe and eccentric in the region of the rearward edge of the sliding shoe can be achieved in especially advantageous manner by making the radius of the sliding shoe slightly greater thanthe radius of the eccentric, butonly by such an extent that an oil wedge capable of: carrying a load can still form in the region of the edges between eccentric and sliding shoe. In this way a clearance between the sliding shoe and the eccentric is also achieved in the region of the forward edge of the sliding shoe, this contributing to the formation of an oil wedge in the region of the forward edge of the sliding shoe.

The invention is illustrated in greater detail in Figures 1 and 2 in which the piston 1 has a hinge part with two hinge eyes 2 at its lower end, said hinge eyes laterally surrounding a hinge eye 3 on the sliding shoe 4. A pin 5 is inserted through the hinge eyes 2 and 3, and makes possible the pivoting movement of the sliding shoe 4 about the piston 1. The sliding shoe 4 is provided in manner known per se with a layer 6 of bearing metal. This layer of bearing metal is somewhat bevelled at the forward edge of the sliding shoe, so that an angle 9,

amounting preferably to l" or less, is formed between the sliding shoe and the eccentric 7, which rotates in the direction of the arrow 8. A corresponding bevel is provided at the rearward edge 4a of the sliding shoe, so

that an angle 9 amounting to approximately 1 or less is formed there also between sliding shoe and eccentric.

The rearward edge of the layer 6 of bearing metal is r limitedby'a bar 10 or the like, which prevents the layer of bearing metal being hammered or squeezed away in the region of the rearward edge. An oil pipe 11 is provided with a series of holes or slots 12, from which oil is sprayed in front of the sliding shoe, The holes or slots are disposed so close beside one another that a uniform layer of oil, is formed underthe sliding shoe in the region of the forward edge thereof.

The forward edge of 6 and the rearward edge of 6 can be achieved in an only slightly modified form by giving the surface of the sliding shoe a somewhat greater radius than the periphery of the eccentric. The magnitude of the angles 9 must, however, be kept so small in any case that an oil film capable of supporting a load can form between the sliding shoe and eccentric or swash plate. The angle is thus much smaller than drawn.

The invention relates not only to sliding shoes having a running surface of soft bearing metal but to sliding shoes in which the running surface consists of aluminium or alloys thereof, of bronze, lead-bronze or the like. The bar 10 can then be omitted in this case.

The invention is of particular importance when the running surface of the sliding shoe is in one piece with or of the same material as the whole sliding shoe.

Aluminium and alloys thereof can, for example, be used for this purpose.

I claim:

1. Means for transmitting reciprocating motion between a reciprocating piston and a rotating member such as aneccentric, comprising: a rigid shoe rockably mounted on the piston and bearing against the surface of the said rotating member with a sliding surface of substantial area fitting snugly to the surface of the rotating member, at least one-fifteenth of the length of the sliding surface of the shoe measured from the rear edge of the shoe not bearing closely upon the surface of the rotating member but extending away from the surface of the rotating member so as to form a wedge angle of not more than about one degree when the greater part of the said shoe surface bears closely on the surface of the rotating member.

2. Means for transmitting reciprocating motion between a reciprocating piston and a rotating member as claimed in claim 1, further comprising a layer of bearingmetal on the sliding surface of the shoe, and a bar of a metal harder and stronger than the bearing metal extending across the sliding surface of the shoe close to its rear edge and forming the boundary-of the layer of bearing metal.

3. Means for transmitting reciprocating motion between a reciprocating piston and a rotating member as claimed in claim 1, the rockable mounting of the shoe upon the piston being constituted by a single central hinge eye on the shoe, two lateral hinge eyes on the piston, and a pin extending through the three hinge eyes.

References Cited in the tile of this patent UNITED STATES PATENTS 1,551,938 Clark. Sept. 1, 1925 1,563,493 Iannes Dec. 1, 1925 1,729,448 Michell Sept. 24, 1929 1,798,508 Tucker Mar. 31, 1931 2,167,882 Fast Aug. 1, 1939 2,631,538 Johnson Mar. 17, 1953 

